1. Field of Invention
The present invention relates to facsimile data transmission. More particularly, the present invention relates to a system and method for minimizing a data bottleneck that may arise during facsimile data transmissions over networks operating at data rates lower than the facsimile data rate.
2. Description of the Related Art
Facsimile (fax) machines have come into widespread use. In 1980, the International Telegraph and Telephone Consultative Committee (CCITT) adopted the Group 3 fax standard. The CCITT recommendations (standards) T.30 and T.4 define Group 3 facsimile service, also known as Group 3 FAX and G3 FAX. The recommendation is for "Group 3 facsimile apparatus." Group 3 facsimile apparatus includes fax machines, computers with fax modems and appropriate software, as well as other products. As referred to herein, the term "FAX machine" applies to any Group 3 facsimile apparatus.
T.30 defines the messages used by Group 3 FAX machines to communicate with one another. This communication includes fax call identification, fax parameter negotiation, training (to verify that higher data rates can be used over a telephone connection), page transmittal, confirmation of reception, and call release. T.4 defines several ways to encode images on a page of a document to be transmitted by a facsimile network.
T.30 was written for facsimile service provided over a wired telephone network, or a Public Switched Telephone Network (PSTN). In such a network, delays are fixed between transmission and reception during a call. Moreover, the data rates supported by the network are always as fast as the facsimile data rates sent over the network. In this environment, T.30 requires strict time constraints between transmissions and responses occurring between communicating FAX machines.
Such time constraints can be difficult to meet when Group 3 facsimile transmissions are attempted over data channels with different characteristics than a wired telephone network. For example, in the wireless environment (e.g., a cellular network), two conditions exist that do not arise during a wired telephone network fax transmission. First, the wireless environment has varying delays between transmission and reception. Second, the data rates over a wireless network are typically less than a wired network and may be less than the rate of fax data transmissions.
When the data rate over the wireless network is less than the fax transmission rate, a data bottleneck will occur between the transmitting FAX machine and the receiving FAX machine (i.e., at the transmission side of the wireless network), causing delay in the fax transmission. Other, non-wireless facsimile networks may also have such a limited data rate and may thus incur data bottlenecks when performing facsimile transmissions. The delays associated with such limited data rate networks can cause T.30 time-outs to expire, resulting in the transmitting FAX machine hanging up during a facsimile call before data transmission is complete. These data channels will be referred to as Low Data Rate Networks (LDRNs), in which the data rates are lower than the fax transmission data rate.
In light of the foregoing, a need exists for an LDRN that can transmit fax data and at the same time minimize data bottlenecks that may arise in the LDRN during fax transmissions.